Use of Gas-Permeable Membranes for the Removal and Recovery of Ammonia from High Strength Livestock Wastewater
Abstract:The recovery of nitrogen (N) from wastes is important in agriculture because of the high cost of commercial N fertilizers. We investigated the use of gas-permeable membranes to capture and recover ammonia from high strength swine wastewaters. The new process includes the passage of gaseous (or free) ammonia (NH3) through a microporous hydrophobic membrane and capture and concentration in a stripping solution on the other side of the membrane. Membrane manifolds are submerged in the liquid and the free ammonia (NH3) is removed from the liquid before it escapes into the air. The concept was tested using concentrated swine manure effluents containing 140 to 1,400 mg/L NH4-N. The use of gas-permeable membranes to remove ammonia from liquid manure was effective, and the rate of N recovery by the gas-permeable membrane system was higher with higher ammonia concentration in the manure. While ammonia gas passed readily through the membrane pores, the soluble COD compounds did not pass. The rate of ammonia recovery was also increased with increased pH of the wastewater. With a pH of 8.3, the rate of N recovery was about 1.2% per hour. This rate was increased 10 times (to 13% per hour) at pH of 10. For liquid manure containing 1,400 mg/L NH4-N, with the membrane manifold installed, in 9 days the total NH4-N concentration decreased about 50%, from 1,290 mg/L to 663 mg/L. As a result, the NH3 fraction in the liquid, which is linked to ammonia emissions, decreased 95%, from 114.2 to 5.4 mg/L. By using the same stripping solution in 10 consecutive batches treating raw swine manure, the recovered N was concentrated in a clear solution containing 53,000 mg/L NH4-N. The results obtained in this study show that the use of gas-permeable membrane technology could be an effective approach to recover ammonia from livestock wastewater. The final products are (1) reduced environmental emissions from livestock facilities and (2) concentrated liquid nitrogen that can be re-used in agriculture as a valued fertilizer.
Document Type: Research Article
Publication date: 2011-01-01
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